A display device has an array substrate. The array substrate has a transparent substrate on which a circuit to apply a display voltage to each pixel is formed. In this array substrate, a defect in a line occurring in a manufacturing step might be a point defect or a linear defect on a display screen. In response, a short-circuit developed between adjacent lines (short-circuit defect) is repaired by cutting and removing a part of the short-circuit and making the lines function normally, for example. A break in a line (breaking defect) is repaired by connecting a part of the break and making the line function normally.
Various methods have been implemented to repair a breaking defect. Meanwhile, ensuring reliability and handling interconnection resistance of a repaired site (repaired part) have been big issues to be solved. Additionally, various considerations have been given on a method of reducing space on the array substrate required for repair or a method of minimizing influence of a repaired part on a product.
A method of repairing a breaking defect occurring in a line on the array substrate is described for example in Japanese Patent Application Laid-Open Nos. 2001-166704 and 9-033937 (1997). According to Japanese Patent Application Laid-Open No. 2001-166704, the number of preliminary lines to be used for repair is reduced. According to Japanese Patent Application Laid-Open No. 9-033937, a repaired part is covered with a seal to avoid an influence of sputter or projection of metal or leakage of light to occur during repair.
Japanese Patent Application Laid-Open Nos. 2001-166704 and 9-033937 are intended to repair a defect in a line in a display region.
Meanwhile, in a display device of recent years, particularly of a type employing COG (chip on glass) mounting, a line from a driver IC to a display region (hereinafter called a leading line) has been thinned considerably in response to higher density of driver ICs and a narrower frame. This makes the occurrence of a break in the leading line likely. Even if the leading line is not broken completely during manufacture, the leading line is still exposed to the danger of a line defect (partial breaking defect) that might lead to a break due to stress such as collision.
Such a defect in a line may be detected during a manufacturing step by an optical defect inspection system (automatic optical inspection: AOI) or an electric defect inspection system (array tester).
However, the leading line cannot be repaired by the techniques of Japanese of Patent Application Laid-Open Nos. 2001-16674 and 9-033937. Additionally, according to Japanese Patent Application Laid-Open Nos. 2001-16674 and 9-033937, repairing lines extend along opposite sides of a display region. This makes the repairing lines long, leading to increase in a resistance value.